The present invention relates to a semiconductor device having a polycrystalline silicon resistor containing oxygen atoms.
Polycrystalline silicon resistors have been widely used in semiconductor devices, and various types have been proposed, for example, by Ming-Kwang Lee et al. entitled "ON THE SEMI-INSULATING POLYCRYSTALLINE SILICON RESISTOR" in Solid-State Electronics Vol. 27, No. 11, 1984, pp. 995-1001, by Takashi Ohzone et al. entitled "Ion-Implanted Thin Polycrystalline-Silicon High-Value Resistors for High-Density Poly-Load Static RAM Applications" in IEEE TRANSACTIONS ON ELECTRON DEVICES, Vol. ED32, No. 9 September 1955, pp. 1749-1756, etc. These resistors employ phosphorus, arsenic and/or boron atoms for determining their resistance values. On the other hand, so-called "SIPOS" (Semi-Insulating Polycrystalline-Silicon) type resistors, in which oxygen atoms are contained in the polycrystalline silicon film with ion-implanted phosphorus or arsenic atoms, have been proposed. The resistance value of the SIPOS type resistor element is determined by the amount of or the density of the oxygen atoms contained in the polycrystalline silicon film, and therefore, a high resistance value can be obtained.
However, when the density of oxygen atoms in the polycrystalline silicon film is a high level, the control of the density is difficult in the process step. Therefore, the resistivity of the polycrystalline silicon film has a large deviation among wafer lots and among polycrystalline silicon films in a wafer. Consequently, a resistor having a higher resistance cannot be obtained with a precise resistance value. On the other hand, if the density of oxygen atoms is set to be low-level and the thickness of the polycrystalline silicon film is thinned to obtain a higher resistance, a precise control of the resistance is also impossible because a silicon oxide layer thermally converted from the surface part of the polycrystalline silicon film must be provided for stabilizing the resistor element, and therefore, the remaining film thickness, which dimension determines the resistance value, is relatively, largely deviated. Specially, the control of the silicon oxide film, that is, the control of the thickness of the remaining polycrystalline silicon film through the oxidation is difficult when the density of oxygen atoms therein is low.
In the prior art SIPOS type resistor element, oxygen atoms are uniformly distributed in the polycrystalline silicon film in the entire thickness. Therefore, a silicon resistor element having a higher resistance value with a precise control is impossible.